1. Field of the Invention
The present invention relates to a liquid ejection method and a liquid ejection apparatus which eject a fine droplet of liquid, and in particular, to a liquid ejection method and a liquid ejection apparatus which are suitably used in the medical field to allow a liquid drug to be sucked into the lungs in the form of a liquid mist.
2. Description of the Related Art
Keen examinations have been made of applications of liquid ejection apparatuses ejecting fine a droplet of liquid, in the fields of ink jet printing and medical care (particularly, the field of drug suction). Various such apparatuses have been proposed.
For example, Japanese Patent Laid-Open No. 2003-154665 discloses a liquid ejection head in which individual liquid chambers and ejection ports through which ink is ejected are coupled together via throttling portions of pore diameter 3 μm to allow a droplet of diameter 3 μm (volume: 0.014 picolitters) to be ejected.
In general, the size of the ejection port (in the example in Japanese Patent Laid-Open No. 2003-154665, the throttling portion pore) is reduced to allow a smaller droplet to be ejected. However, when the size of the ejection port, that is, the diameter thereof, is smaller than 10 μm, the liquid in the ejection port changes rapidly as a result of drying or the like, hindering the liquid from being properly ejected. Furthermore, if a recovery process is frequently executed to maintain proper liquid ejections, costs are increased, and ink is wastefully discharged. Thus, in the field of ink jet printing, little effort has been made to provide products with the ejection port of diameter at most 5 μm.
According to the technique disclosed in Japanese Patent Laid-Open No. 2003-154665, a relatively large ejection port is provided outside a small throttling portion pore of diameter about 3 μm. Fluctuation of the liquid surface of a meniscus in the liquid formed in the ejection port seriously affects a direction in which a very small droplet of diameter 3 μm (volume: 0.014 picolitters) fly. This also discourages effort to develop products with the ejection port of diameter 3 μm. However, in the field of drug suction, variation in the flying direction of liquid droplet is somewhat allowable.
On the other hand, in the development of a technique for reducing the size of the ejection port (in the example in Japanese Patent Laid-Open No. 2003-154665, the throttling portion pore) and thus the size of the ejected liquid droplet, an increase in the flow resistance of the liquid hinders the droplet from being properly ejected. Thus, in the conventional art, the minimum possible diameter of the throttling portion pore is about 3 μm. A thin throttling portion of thickness 1 μm may be damaged or broken by the flow of the liquid during ejection. Furthermore, if an ejection port of a relatively large diameter is formed outside the throttling portion pore as in the case of Japanese Patent Laid-Open No. 2003-154665, the liquid in the ejection port needs to be raised upon being ejected to the exterior. This hinders the liquid from being properly ejected. Thus, in the conventional art, making the diameter of the throttle portion pore smaller than 3 μm is difficult.
Japanese Patent Laid-Open No. 2005-231086 discloses a liquid ejection head with an ejection port and a throttling portion pore similar to those in Japanese Patent Laid-Open No. 2003-154665. As described in Japanese Patent Laid-Open No. 2005-231086, setting the diameter of the throttling portion pore to about 3 μm increases time required to complete refilling the liquid. Thus, in the conventional art, also in connection with the refilling of the liquid, making the diameter of the throttle portion pore smaller than 3 μm is difficult.
In the field of drug suction, there has been a demand for a liquid ejection apparatus which enables a small droplet of diameter 10 μm (volume: 0.5 picolitters) to be ejected and which allows a sufficient number of liquid droplets to be ejected per unit time without improperly ejecting the liquid as a result of possible drying.